THE SUPPRESSION OF OVARIAN CYCLICAL ACTIVITY IN GROUPS OF MICE, AND ITS DEPENDENCE ON OVARIAN HORMONES

Abstract

Department of Physiology, University Medical School, Teviot Place, Edinburgh EH8 9AG (Received 14th March 1975) The oestrous cycle of the mouse is influenced by environmental conditions (Merton, 1937; Van der Lee & Boot, 1955, 1956; Dewar, 1959). Contact with intact, but not castrated, male mice shortens the oestrous cycle (Whitten, 1958; Bruce, 1965). This effect is due to an olfactory pheromone in the urine of male mice (Parkes & Bruce, 1962; Marsden & Bronson, 1964; Bronson & Whitten, 1968). Isolated females usually have cycles 4 to 6 days long, but, if the females are caged in groups, the cycles become more irregular (Andervont, 1944; Whitten, 1957, 1959). Whitten (1966) suggested that this effect might be due to a female pheromone. Champlin (1971) has shown that oestrus is less frequent in a single female placed in a cage previously soiled by a group of females. In view of the finding of